1. Field of the Invention
The present invention relates to an interferometric method for detecting information about a sample and a digital holographic microscope.
2. Description of the Related Art
There are two major methods for a digital holographic microscope which uses holograms to reconstruct an image of an object. One is a phase shift method (i.e., on-axis method), and the other is an off-axis method.
The on-axis method usually requires a plurality of holograms (e.g., four holograms) to observe the object from a direction and reconstruct the object image, because only one hologram cannot show whether the phase of the incident beam is delayed by the existence of the object.
Accordingly, the plurality of holograms are formed by using several reference beams whose phases are than different each other. In the on-axis method, the light intensity information of an image on the detector, which is obtained with each reference beam, is used for reconstructing the image of the object.
On the other hand, the off-axis method doesn't require such several holograms to reconstruct the image. In the off-axis method, an interference pattern formed by a reference beam and an object beam is used for reconstructing the image of the object.
The measurement time for the on-axis method can take, for example, four times longer than the off-axis method in light of the number of the holograms.
Since a plurality of holograms, which are obtained with various illumination angles to the object, are necessary to execute three-dimensional tomographic measurement of a phase object, the off-axis method may be selected in view of the measurement time.
Applying the off-axis method to the field of three dimensional measurements is a relatively new technique, and the technique is not matured yet. Accordingly, there is a need for an optical measurement system using the off-axis method for three dimensional measurements.